Field of the Invention
The present invention relates to a semiconductor light-receiving device.
Background Art
High-speed response avalanche photodiodes for optical communication use AlInAs for an electron multiplication layer. Among them, avalanche photodiodes are being developed in recent years, for which a p-type contact layer, a light absorption layer, a p-type field alleviating layer, an electron multiplication layer and an n-type contact layer are made to grow in order on a semi-insulating InP substrate (e.g., see Japanese Journal of Applied Physics 51 (2012) 02BG03). Such a structure has an excellent high-speed response characteristic, but on the other hand, Fe contained in the semi-insulating InP substrate and Zn in the p-type contact layer are likely to trigger mutual diffusion, and this may adversely affect the device yield (e.g., see Journal of Applied Physics 84 (1998) 8).
Particularly when a plurality of diodes are formed, arranged side by side on a substrate, the above-described mutual diffusion between Fe and Zn makes it fail to sufficiently separate one diode from another, resulting in a problem of producing a leakage current. In order to solve this problem, an undoped InP layer may be made to grow into a thick buffer layer on an Fe-doped semi-insulating InP substrate to thereby separate the substrate from the p-type contact layer. However, in the InP buffer layer, it is not possible to suppress influences of impurity such as Si remaining in an interface between an epitaxial layer and the substrate, and it is not possible to suppress a leakage current, either. Furthermore, the growth time period of the buffer layer is extended, and this is not desirable from the standpoint of productivity such as an amount of material consumption. Moreover, incident light may be absorbed in the buffer layer, causing light-receiving sensitivity to deteriorate.